The present invention relates to the field of ignition sources and more particularly to ignition sources used in internal combustion engines.
In the field of internal combustion engines, especially the reciprocating type, a measured quantity of fuel and air is compressed and ignited either by an external ignition source or by the heat of compression. The engine in which the air/fuel mixture is ignited by the heat of compression is commonly called a diesel engine. It utilizes a system where the air for combustion is compressed to an elevated temperature sufficiently high to ignite the fuel supplied from a fuel injection source. Such fuel injection source is typically an injector having a tip exposed to the combustion chamber and which sprays fuel in discrete streams. The fuel injector injects the fuel either in a radiating pattern from a central location or in a given direction to promote mixing by swirl of the combustion chamber air. However, in either case, the injection of fuel and the resultant initiation of combustion is begun substantially at or adjacent a point.
Recent developments in the field of homogenous charge compression ignition engines have proposed injecting fuel into the intake air prior to compression and using various schemes to ignite the resultant mixture. Such proposal usually involves a point ignition source such as a sparkplug.
By far the most common engine type on the road is the spark ignited gasoline engine. The gasoline engine was first developed in the latter part of the 19th Century and has since been employed widely for powering passenger vehicles owing to its relatively quiet operation and starting ease. With the advent of increasing energy prices and customer demand, the spark ignition engine is being asked to do significantly more than it was in prior years. Gasoline engine developments have, for the most part, focused on carrying a maximum flow of air efficiently into the combustion chamber and exhausting the products of combustion after the combustion event occurs. Developments like multiple valves, tuned intake systems, variable geometry intake systems, and positive charging of the intake charge by a turbocharger or supercharger are common approaches used to try and improve air flow.
Correspondingly, the fuel system has evolved and developed through the use of injectors. The injectors have been electronically controlled to vary the quantity and timing to produce highly flexible injection of fuel into the mixture for combustion. Additional proposals have been made for injecting fuel directly into the combustion chamber similar to a system mechanically implemented on early Mercedes Benz sports cars.
Recently, biofuels have been proposed that use various forms of ethanol or methanol from grain crops, cellulous fiber or vegetable matter thereby providing a renewable resource. Such fuels offer the advantage of high octane ratings so that higher compression ratios may be easily handled within the combustion chamber. They also permit a significant reduction in emissions. However, one drawback with fuels of this type is the slow propagation of the flame front making it necessary for ignition timing to be well in advance of top dead center (TDC) to be sure all of the mixture is combusted. This in turn reduces efficiency as the combustion pushes in one direction against the piston that is moving in the opposite direction as it moves toward TDC.
The sparkplug is a common igniter used to initiate combustion of a fuel air mixture in a spark ignition engine. Various developments over the years have increased the energy passing across the spark gap so that it more efficiently promotes combustion. In addition, some inventors have suggested enhancing the ignition by subjecting the spark gap to electromagnetic forces to, in effect, widen the area over which combustion is initiated.
However, most of these approaches still suffer from the limitation that they are in fact point, or near point, initiators of combustion.
Another problem exists related to diesel engines and their inability to start in cold weather. As noted above, a diesel engine utilizes the heat of compression to ignite the air/fuel mixture in the combustion chamber. However, when the cylinder head and cylinder block are cold, they serve as a heat sink, absorbing a portion of the heat generated by the compression. Currently, glow plugs are utilized to heat the engine block and surrounding cylinders. Because glow plugs are essentially resistive loads that emit heat when a current is run through them, the pre-heating process can take some time: up to 20 seconds. Therefore, there exists a need for quicker and more efficient heating of diesel engine blocks in cold weather conditions.